Pairs or triplets of charged particles separated by distances of a few hundred nanometers are more effective at both cell killing and the induction of chromosome aberrations than randomly incident particles. The effectiveness of these associated ions decreases as the particle separation increases in a way that sheds light on the interaction of sub-lesions that leads to the observable endpoints of cell lethality and aberration production. Future experiments will be designed to extend previous studies to incude T1 cells of human kidney origin and a human radiation-sensitive ataxia telangiectasia cell line. Attempts will also be made to determine the effects of associated ions in the incidence of oncogenic transformtions in C3H 10T1/2 cells in order to shed light on the mechanism of radiation carcinogenesis. The principal objective of these experiments is to employ pairs or triplets of particles produced by a molecular ion beam to determine the effects of spatial distribution of absorbed radiation energy on cell killing, chromosome damage and cell transformation. The experiments should provide information on the distribution of DNA in the interphase nucleus.